Dinosaurs are a group of reptiles that dominated the land for over 140 million years (more than 160 million years in some parts of the world). They evolved diverse shapes and sizes, from the fearsome giant Spinosaurus to the chicken-sized Microraptor, and were able to survive in a variety of ecosystems.

One of the reasons for dinosaurs' success is that they had straight back legs, perpendicular to their bodies. This allowed them to use less energy to move than other reptiles that had a sprawling stance like today's lizards and crocodiles.